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par-projectioncourbe-en.tex
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\section{Curves of real-valued and \Index{parameterised functions}}
\subsection{Curve of a real-valued function}
The object \Lkeyword{courbe} allows us to draw a curve, where the
name is given with the option \Lkeyword{function}. This \Index{function},
with values in $\mathbb{R}$, has to be defined by the macro
\verb+\defFunction+ (see the appropriate paragraph for more
details).
We can define this function either in algebraic notation, with the
option \Lkeyword{algebraic}, or in Reverse Polish Notation (RPN),
with variables like $(x,u,t\ldots)$, using an expression of the
following form:
\begin{verbatim}
\defFunction[algebraic]{nom_fonction}(x){x*sin(x)}{}{}
\end{verbatim}
\begin{verbatim}
\defFunction{nom_fonction}(x){x dup sin mul}{}{}
\end{verbatim}
\encadre{This expression needs to be included within a
\texttt{pspicture} environment.}
The limits of the variables are defined by the option
\texttt{\Lkeyword{range}=$xmin$ $xmax$}, and the option \texttt{argument=$n$}
defines the number of points to be plotted when drawing the \Index{curve}.
\begin{LTXexample}[width=7.5cm]
\begin{pspicture}(-3,-3)(4,3.5)%
\psframe*[linecolor=blue!50](-3,-3)(4,3.5)
\psset{lightsrc=50 20 20,viewpoint=50 30 15,Decran=60}
\psset{solidmemory}
\defFunction[algebraic]{1_sin}(x){2*sin(1/x)}{}{}
\psSolid[object=grille,
base=-3 0 -3 3,
linewidth=0.5\pslinewidth,linecolor=gray,]
%% definition du plan de projection
\psSolid[object=plan,
definition=equation,
args={[1 0 0 0] 90},
base=-3.2 3.2 -2.2 2.2,
planmarks,
showBase,
name=monplan]
\psset{plan=monplan}
\psSolid[object=plan,
args=monplan,
linecolor=gray!40,
plangrid,
action=none]
\psProjection[object=courbe,
linecolor=red,
range=-3 3,resolution=720,
function=1_sin]
\composeSolid
\axesIIID(4,2,2)(5,4,3)
\end{pspicture}
\end{LTXexample}
\subsection{\Index{Parameterised curves}}
The technique used here is analogous to the above, with the
difference that the values now come from $\mathbb{R}^2$, and the
object for the macro \Lcs{psProjection} is now \Lkeyword{courbeR2}.
For example, to draw a circle of radius $3$ and centre $O$, we
type:
\begin{verbatim}
\defFunction[algebraic]{cercle}(t){3*cos(t)}{3*sin(t)}{}
\end{verbatim}
Another example: \Index{Lissajous} curves.
\begin{LTXexample}[width=7.5cm]
\begin{pspicture}(-3,-3)(4,3.5)%
\psframe*[linecolor=blue!50](-3,-3)(4,3.5)
\psset{lightsrc=50 20 20,viewpoint=50 30 15,Decran=60}
\psset{solidmemory}
\defFunction[algebraic]{F}(t){2*sin(0.57735*t)}{2*sin(0.707*t)}{}
\psSolid[object=grille,
base=-3 0 -3 3,
linewidth=0.5\pslinewidth,linecolor=gray,]
%% definition du plan de projection
\psSolid[object=plan,
definition=equation,
args={[1 0 0 0] 90},
base=-3.2 3.2 -2.2 2.2,
name=monplan,
planmarks,
showBase]
\psset{plan=monplan}
\psSolid[object=plan,
args=monplan,
linecolor=gray!40,
plangrid,
action=none]
\psProjection[object=courbeR2,
range=-25.12 25.12,resolution=720,
normal=1 1 2,linecolor=red,
function=F]
\composeSolid
\axesIIID(4,2,2)(5,4,3)
\end{pspicture}
\end{LTXexample}
\endinput

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